(1) Field of the Invention
The present invention relates to an image forming apparatus for multi-color printing using the electrophotography and particularly relates to an image forming apparatus capable of image forming in appropriate conditions even if a plurality of developing units are arranged in an arbitrary order.
(2) Description of the Prior Art
Recently, there has been a tendency toward colorization in the field of image forming apparatus such as copiers and the like, and color copiers have widely been put on the market. In such color copiers, four color, namely black, cyan, magenta and yellow developers are used and the multiple number of developing units storing the different color developers are arranged in a certain relationship.
Conventionally, upon the replacement of the developing units for such an image forming apparatus having multiple developing units, the operator should confirm the developer's color being stored in a developing unit and attach the unit to the predetermined developing unit mounting space on the apparatus body. This configuration not only provides the operator with a burden, but also has frequently induced deficiencies and accidents due to erroneous insert or damages to the parts.
In a color image forming apparatus wherein a multiple number of color image developing units each having a different color of toner are arranged in series in the paper conveyance direction, color components of an image are formed by associated color image developing units and superimposed on a sheet of paper as the paper is conveyed. The paper with the toner image formed thereon in a superimposed manner after the passage of the all the color image developing units is made to pass through the heated, heat roller in the fixing unit so that the toner becomes fused by heat from the roller surface, to thereby complete image formation.
The order or position in which the color image developing units are inserted and set in the main body determines the order of transfer and superimposition. That is, the color toner of the color developing unit laid out on the most downstream side in the transfer and superimposition stage will adhere to the topmost layer of the print paper so that it will be most affected by the heat from the heated surface of the heat roller of the fixing unit. Resultantly, the conventional configuration has the following problem. That is, if the order of insertion of the developing units or the order in which the color toners are superimposed is changed, color or hue in the printed image will vary depending upon the order of superimposition of the color toners.